Simulation Of Adsorption Process Research Articles

Adsorption Thermodynamics for Process Simulation.

Adsorption has rapidly evolved in recent decades and is an established separation technology extensively practiced in gas separation industries and others. However, rigorous thermodynamic modeling of multicomponent adsorption equilibrium remains elusive, and industrial practitioners rely heavily on expensive and time-consuming trial-and-error pilot studies to develop adsorption units. This article highlights the need for rigorous adsorption thermodynamic models and the limitations and deficiencies of existing models such as the extended Langmuir isotherm, dual-process Langmuir isotherm, and adsorbed solution theory. It further presents a series of recent advances in the generalization of the classical Langmuir isotherm of single-component adsorption by deriving an activity coefficient model to account for the adsorbed phase adsorbate-adsorbent interactions, substituting adsorbed phase adsorbate and vacant site concentrations with activities, and extending to multicomponent competitive adsorption equilibrium, both monolayer and multilayer. Requiring a minimum set of physically meaningful model parameters, the generalized Langmuir isotherm for monolayer adsorption and the generalized Brunauer-Emmett-Teller isotherm for multilayer adsorption address various thermodynamic modeling challenges including adsorbent surface heterogeneity, isosteric enthalpies of adsorption, BET surface areas, adsorbed phase nonideality, adsorption azeotrope formation, and multilayer adsorption. Also discussed is the importance of quality adsorption data that cover sufficient temperature, pressure, and composition ranges for reliable determination of the model parameters to support adsorption process simulation, design, and optimization.

Five definitions of adsorption and their relevance to the formulation of dynamic mass balances in gas adsorption columns

Numerous dynamic mass balances in the literature that describe the adsorption of gases in a column are written in terms of actual or absolute adsorption, while unwittingly and incorrectly utilizing excess adsorption isotherms. Perhaps this is because the actual and absolute adsorption isotherms cannot be experimentally measured nor predicted without making uncertain assumptions. The objective here was to derive unambiguous relationships between actual, absolute, excess, net and column amounts adsorbed that provide a straightforward understanding of the subtle differences between these quantities and that provide a simple means for incorporating them into dynamic mass balances. For this purpose, the actual, absolute, excess, net and column amounts adsorbed (loadings) were clearly defined, along with various volumes, porosities and densities that exist inside and outside an adsorbent contained in a column with a gaseous adsorbate. These adsorption definitions and quantities were used to derive four interconversion relationships for each type of adsorption in terms of the actual loading. The resulting expressions, based on intensive properties, can be used to relate any adsorption definition to any other adsorption definition. These relationships were also used to derive five dynamic mass balances, one for each type of adsorption. The similarities and differences in the terms between each of these five dynamic mass balances were discussed, along with their applicability to real world problems. In some cases at low pressure where the isotherms do not differ appreciably, it may be approximately correct to use excess or net adsorption isotherms in a dynamic mass balance written in terms of actual or absolute adsorption. However, the extent of the incorrectness is unknown due to mass transfer effects. So, it is recommended to use the dynamic mass balance with its specific type of adsorption, most likely excess adsorption. Then, when certain assumptions are made about the adsorbing and non-adsorbing void fractions, these expressions can be readily used in adsorption process simulation.

Numerical simulation of adsorption process of O2/H2O mixed gas in coal porous media

It is of great significance for coal mining and utilization to study the adsorption process of mixed gas in coal. In this paper, the Monte Carlo method (MC) is employed to study the competitive saturation adsorption of oxygen and water vapor inside coal particles, and then the convection, diffusion and adsorption inside and between particles are studied by lattice Boltzmann method (LBM). In addition, this study examines the impacts of porosity, average particle size, and gas concentration on the process of adsorption in coal porous media. The research results show that oxygen and water vapor present in the mixed gas experience increased permeability, diffusion rate, and saturated adsorption capacity as the porosity and average particle size of the coal porous medium increase. However, the time required to achieve saturated adsorption decreases. Under the condition of maintaining the proportion of gas components and altering the initial gas concentrations from 4.087 to 53.131 mol/m3, saturated adsorption capacity of both gases remains nearly unchanged. Yet, the effective diffusivity of gases declines with increasing initial concentration. Additionally, it is also found that water vapor diffuses more quickly than oxygen in the mixed gas and achieves adsorption saturation faster.

Modeling of multi-temperature Type I and II benzene/ammonia adsorption isotherms: Dual LF model and linearized DR model

Adsorption isotherm is basic data for evaluating the porous adsorbent adsorption capacity and explaining gas–solid adsorption behavior. Adsorption equilibrium modeling is a simple method to describe isotherm data in application. In this paper, taking C6H6 and NH3 as an example, multi-temperature Type I or Type II adsorption isotherms on AC, ASZMT, and 13X were investigated and fitted. Results show that C6H6 and NH3 adsorption behaviors on 13X both existed in chemisorption. At certain adsorbed capacity, the isosteric heats are higher than 50 kJ·mol−1. Type I and Type II C6H6 or NH3 adsorption isotherms could be successfully described using the extended Dual LF model·NH3 temperature-independent characteristic curves on AC and ASZMT were obtained using the Linearized DR model and successfully used to predict NH3 adsorption data at any pressure within the whole room temperature. Further, the Dual LF model was extended to describe other adsorption isotherms including IUPAC Type III, IV, and V. The R2 between the model and data were higher than 0.98, proving that it has universal applicability than other classical models such as Langmuir, Freundlich, Toth, and so on. It has the potential to be used as a general equilibrium model for adsorption process simulation in the future.

Molecular Simulation of Adsorption Process of CH4 and C2H6 in Kaolinite Slits

Molecular Simulation of Adsorption Process of CH4 and C2H6 in Kaolinite Slits

Simulation of adsorption processes on moving particles based on an Euler-Euler description using a lattice Boltzmann discretization

In this paper an adsorption model is applied to moving solid particles in the carrier fluid using the Euler-Euler approach discretized with the lattice Boltzmann method and implemented in the OpenLB open source software library. The adsorption model is based on mass transfer as described by the linear driving force model and can incorporate several mass transfer mechanisms, such as film diffusion, surface diffusion and pore diffusion. Particles, their adsorbate loading, and the solute are described by the advection diffusion equation with an adsorption source term. The novel Eulerian lattice Boltzmann adsorption model is validated numerically using analytical solutions for a batch and fixed bed reactor. Grid studies are conducted to show the convergence of the model. The applicability of the model to complex flow problems is demonstrated in a static mixer with moving particles.

Simulation of gas-solid adsorption process considering particle-size distribution

• Population balance equation (PBE) is combined with particle-dependent adsorption kinetics equations to simulate gas-solid adsorption process on adsorbent with particle-size distribution. • Simulation results show that the adsorption behavior is significantly affected by the particle-size distribution of the adsorbent. • Approximation of particle-size distribution to volume-average size may lead to large underestimation of adsorption periods. The particle-size distribution of adsorbents usually plays an important role on the adsorption performance. In this study, population balance equation (PBE) is utilized in the simulation of an adsorption process to model the time-dependent adsorption amount distribution on adsorbent particles of a certain size distribution. Different adsorption kinetics model can be used to build the adsorption rate function in PBE according to specific adsorption processes. Two adsorption processes, including formaldehyde on activated carbon and CO 2 /N 2 /CH 4 mixture on 4A zeolite are simulated as case studies, and the effect of particle-size distribution of adsorbent is analyzed. The simulation results proved that the influence of particle-size distribution is significant. The proposed model can help consider the influence of particle-size distribution of adsorbents on adsorption processes to improve the prediction accuracy of the performance of adsorbents.

Simulation of Adsorption Process of l-Tryptophan on Mixed-Mode Resin HD-1 with Combined Physical Adsorption and Ion Exchange.

The mass-transfer process of l-tryptophan (l-Trp) in the hydrophobic interaction/ion-exchange mixed-mode resin HD-1 particles and fixed bed was studied experimentally and theoretically. The adsorption kinetics of l-Trp in single-component and multicomponent adsorption systems was investigated under different pH conditions. The co-adsorption of sodium ions (Na+) and l-Trp anions was found to be negligible. A modified liquid-film linear driving force model considering the physical adsorption of l-Trp zwitterions and anions as well as ion exchange of l-Trp cations was proposed. The dissociation equilibria of l-Trp molecules and functional groups on the resin were introduced in the model. The model could well fit the kinetic adsorption curves of l-Trp at different pH values. The presence of Na+ and the impurity amino acid l-glutamic acid (l-Glu) did not significantly affect the mass-transfer rate of l-Trp. The dynamic adsorption processes of l-Trp under different pH and concentration conditions were studied. A modified transport-dispersive model considering axial diffusion, liquid-film mass transfer, and a combined physical adsorption and ion-exchange equilibrium was established, which could predict the adsorption breakthrough curves of l-Trp well. During the dynamic adsorption process, the pH of mobile phase in the fixed bed changed with changing the l-Trp concentration in the mobile phase. l-Trp was well separated from Na+ and l-Glu with the purity of l-Trp higher than 99%, the recovery rate higher than 95%, and a concentration of 4.69 × 10–3 mol/L. The elution chromatographic peaks of l-Trp, l-Glu, and Na+ and the pH of the outlet solution were predicted satisfactorily.

Modeling and gPROMS based simulation of adsorption process for the removal of Cu (II) from aqueous wastewater

The present work studies the performance of Indion 730 (Strong acid) ion exchange resin for the removal of Cu (II). The modeling and gPROMS based simulation is used to study the sorption capacity, equilibrium, and performances of Indion 730 ion exchange resin. The extraction effectiveness of the resin is studied by using breakthrough curves. The experimental and simulation results were compared. A numerical model is proposed for the investigation of the ion exchange phenomenon using gPROMS using various optimized parameters like flow rate, bed height, and initial concentration of wastewater containing Cu (II) heavy metal ion in the column. For instance, the effects of flow rate, bed height, and inlet concentration of heavy metal on a breakthrough curve are investigated in depth. The results illustrate that the predicted theoretical breakthrough curves show analogous patterns with the corresponding investigational output with a discrepancy of the equilibrium time. The predictions of the model will help to discover the optimal conditions of operation.

Integrated material and process evaluation of metal–organic frameworks database for energy-efficient SF[formula omitted]/N[formula omitted] separation

In this work, we proposed multi-scale screening, which employs both molecular and process-level methods, to identify high-performing MOFs for energy-efficient separation of SF6 and N2 mixture. Grand canonical Monte Carlo (GCMC) simulations were combined with ideal adsorption process simulation to computationally screen 2890 metal–organic frameworks (MOFs) for adsorptive separation of SF6/N2. More than 150 high-performing MOFs were identified based on the GCMC simulations at the pressure and vacuum swing conditions, and subsequently evaluated using the ideal adsorption process simulation. 78 out of 86 MOFs selected for the VSA conditions were able to achieve the 90% target purity level of SF6, but 62 top-performing MOFs selected for the PSA condition could not reach the purity level with a single train PSA configuration. Cascade PSA configuration was proposed and adopted to improve the purity level. We also investigated the effect of vacuum pump and compressor efficiency on the energy consumption of the process. We found that the top-performing MOFs were able to achieve the 90% purity-level of SF6 with 0.10–0.4 and 0.5–1.4 MJ per kg of SF6 for VSA and PSA processes, respectively. Finally, the process-level performance of top-performing MFOs (HKST-1, UiO-67) was evaluated on the basis of the experimental isotherms obtained from the literature, and compared with the other materials reported in the literature (MIL-100(Fe), UiO-66, and zeolite-13X). We found that the results based on the experimental isotherms are in qualitative agreement with the results based on the simulated isotherms.

Computational fluid dynamics simulation of adsorption process in a liquid-solids fluidized bed

For simultaneously predicting the hydrodynamics and protein adsorption process in a liquid-solids fluidized bed (LSFB), a computational fluid dynamics (CFD) model is established by combining the two-fluid model (TFM) for the liquid-particles two-phase fluidization system with the c2¯−εc model for the turbulent mass transfer. In terms of hydrodynamics, the kl−εl−kp−εp−Θ equations are adopted to describe phases turbulence. The simulations of hydrodynamics using various drag models and different modelling parameters are conducted to test their sensitivity. Then for the adsorption process, the recently developed formulations of the c2¯−εc model are adopted to characterize rigorously the turbulent mass diffusion in LSFB. With the proposed model, the velocity field as well as the concentration field can be acquired. Simulated results are compared with the experimental data and a good agreement between them is found.

Molecular dynamics simulation of adsorption processes on the surface of ZnO nanoclusters

This work carried out research of the adsorption processes of O2 molecules on ZnO nanoclusters under different initial conditions by molecular dynamics method. To describe the interaction between atoms, we used the reactive force field (ReaxFF) interatomic potential. Several computer experiments were conducted with different initial conditions. We have been found that the whole process of adsorption was divided into two stages, the first stage was characterized by a rapid increase in the number of adsorbed molecules, the second one an increase of fluctuations in the change of adsorbed molecules on the surface over time. The higher gas pressure in the system corresponds to the greater number of O2 molecules diffusing into the volume of the ZnO nanocluster, therefore, the crystal structure of the surface of the ZnO nanocluster becomes amorphous. In addition, it was established that the tendencies of distribution of the dependence of the central symmetry parameter with the oxygen concentration in the system (NO2 < 100 molecules) were similar. The situation was quite different when the number of oxygen molecules increased: the value of the central symmetry parameter of surface atoms was more evenly distributed, which cannot be considered as a crystalline state of ZnO nanocluster.

Adsorption–Desorption Behaviors of Methanol and Ethyl Acetate on Silica Gel: Modeling and Experimental Tests

Methanol and ethyl acetate are typical oxygen-containing volatile organic compounds which are widely used in industry, often leading to serious pollution. Herein, the adsorption–desorption hybrid process has been applied to recover and recycle the methanol and ethyl acetate waste gases using micro–mesoporous silica gel. Results show that compared with commercial activated carbons, the silica gels perform better (85%) in adsorbing the methanol and ethyl acetate due to their stronger affinity. Further tests show that competitive adsorption happens between them. The silica gel shows stronger affinity to ethyl acetate than to methanol. It is also found that an increase in the flow rate and concentration could facilitate the mass transfer of the substances in the pores of the silica gels. Based on the tests, an adsorption process simulation method with ideal adsorption solution theory and the linear driving force model has been applied to simulate the overshoot behaviors of breakthrough curves for the dynamic adsorption of this binary mixture on silica gels (error in ±7%). In this way, the concentration distribution of each adsorbed component on the solid phase in the adsorption bed has also been visualized and analyzed, which was validated by experimental tests. A dynamic adsorption model has been proposed to describe the adsorbed multicomponents on the solid phase for the adsorption of mixture. Finally, according to the adsorption and desorption profiles, a temperature swing–pressure swing combined process is proposed to desorb the adsorbed methanol–ethyl acetate mixture.

Multiscale Simulation of Adsorption Based Microcantilever Biosensors for Radiation Exposure Effects.

Background: This article is focused on biological measurements based on molecular interactions. The specific biomarker implemented for radiation biosensor is FLT3, which bears changes in the body regarding radiation exposure. Experimental results of sensing vancomycin verify the overall results of two steps of numerical methods for different scales.Objectives: The aim is to provide adequate modeling procedures to predict sensory data. Multiscale modeling is implemented to simulate molecular interaction and its consequent micro mechanical effects. The method is implemented to calculate surface traction of microcantilever biosensor.Materials and Methods: The method consists of molecular dynamics simulation of adsorption process by implementing classical mechanics theory to calculate the final response of the sensor as tip deflection. The sequential information transaction is assumed between the physical parameters of two governing scales. The numerical method consists of the location of particles providing for a nano-metric periodic boundary conditioned functionalized surface implemented, and the numerical thermodynamic formula is, in turn, use energy parameters to acquire macro-mechanical deflection of a specific microcantilever. Also, novel sensitivity analysis of the results as the adsorption process moves toward more saturated substrate provided.Results: Verification of the simulation method for Vancomycin sensing results enjoys less than 20 percent of deviation regarding the experimental data. The standard deviation of 0.054 in the final expected response of the sensor is calculated as the accuracy of the radiation biosensor based on FLT3.Conclusions: The method is still to reach a correlation between the concentration of target molecules in solution and the number of adsorbed molecules per area of the sensor. A scaled correlation between sensor’s response and the amount of biomarker is found using tip deflection of a sample designed microcantilever. Around one micrometer deflection that can be read out using various conventional methods was observed at saturation of adsorption surface. The analyses provide adequate data to design a sensor capable of measuring the effect of cosmic radiation to the human body.

Importance of Incorporating a Vacuum Pump Performance Curve in Dynamic Adsorption Process Simulation

The importance of incorporating a vacuum pump performance curve into a mathematical model that describes the regeneration steps in a vacuum swing adsorption (VSA) cycle was assessed. This was accomplished by evaluating the relationship between pressure and flow rate at the exit of a 13X zeolite bed, initially and uniformly saturated with 70 vol% CO2 in N2 at 333.15 K and 1 atm, which then underwent just countercurrent depressurization (CnD) and light reflux (LR) steps, i.e., the regeneration steps in a VSA cycle. Overall, this study revealed it is imperative to use a realistic vacuum pump model in cyclic adsorption process simulation, especially for estimating the ideal isentropic energy consumed during the regeneration steps in a VSA cycle, and it revealed the possible inaccurate performance predictions that might result when using a valve equation alone to describe these steps. The study on the effect of valve size (cv) without the vacuum pump present to mimic the behavior of the vacuum pump performance...

Simulation of Adsorption Process in a Rotary Solid Desiccant Wheel

Simulation of Adsorption Process in a Rotary Solid Desiccant Wheel

Research progress in the characterization of protein adsorption on biomaterial surface

The characterization methods in the field of protein adsorption on biological materials in recent years were reviewed from the aspects of protein adsorption amount, adsorption layer thickness, molecular conformational change after protein adsorption, molecular morphology after protein adsorption, and protein molecule adsorption process simulation. These methods include biochemical analysis, surface plasmon resonance (SPR), dissipative quartz crystal microbalance (QCM-D), ellipsometry (ELM), optical interference reflection (RIFS), attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR), circular dichroism (CD), atomic force microscopy (AFM) and computer molecular simulation techniques. In this paper, the basic principles, the advantages and disadvantages of the above characterization methods and related researches were reviewed. This paper provides a comprehensive and reliable basis for the selection of protein experimental characterization methods in protein adsorption, biomaterial design and other research, and provides new ideas for research in the field of protein. Key words: Protein; Adsorption; Biomaterial; Characterization

CFD Simulation of Silica Gel as an Adsorbent on Finned Tube Adsorbent Bed

The adsorption technology is becoming the more expected solution by today’s researchers for fix the energy and environmental issues. The main part of the cooling system adsorption is adsorbent and adsorbate. One of the most widely used adsorbents in research of adsorption technology is silica gel. A new silica gel-water adsorption chiller design was developed that composed of two sorption chambers with compact fin tube heat exchangers as adsorber, condenser, and evaporator. Energy, mass, and momentum conservation equations of the adsorption systems have been used for the CFD two and three dimensional models. The geometry of simulation is simply made within silica gel layer between two fins. The simulation is also implemented using a finite volume method through the CFD software Fluent. User defined functions are given to modify the energy, mass, and momentum conservation equations. The simulation of adsorption process is adjusted at unsteady condition. Adsorption and desorption processes are simulated with room temperature for cooling water inlet at temperature 305.15 °K, hot water inlet at temperature 353.15 °K, mass flow rate cooling water inlet at 0.3 kg/s and pressure 32 KPa. For the whole adsorbent bed area, the result shows that the highest absolute adsorption rate at the outer surface, while the lowest rate is at the center. After adsorption was finished, the condition is reversed. The highest absolute adsorption rate is achieved at center, while the lowest rate is achieved at the outer surface.

New Kinetic Model That Describes the Reversible Adsorption and Desorption Behavior of CO2 in a Solid Amine Sorbent

Five, semi-empirical, temperature-dependent, kinetic models were developed and systematically studied to determine which one best described the reversible reaction/adsorption and desorption behavior of CO2 in a solid amine sorbent over a broad range of experimental conditions. Each model varied in the number and type of reaction to account for different CO2–amine site reactions. The solid amine sorbent was composed of polyethylenimine (PEI) immobilized on a CARiACT G10 silica support. A total of 4 temperatures (40, 60, 80, and 100 °C) and 7 concentrations of CO2 in N2 at 1 atm (1.2, 4.8, 14.5, 32.8, 56.1, 69.8, and 88.6 vol %) were studied by carrying out 4 consecutive adsorption/desorption cycles at each of the 28 conditions using a thermogravimetric analyzer (TGA). Each cycle consisted of 40 min of adsorption in CO2/N2 followed by 40 min of desorption in N2. The best model consisted of three parallel reactions, which was consistent with PEI having three different amine sites. Considering the wide range of conditions studied, this is a first-of-its-kind, kinetic model that should prove to be very useful in an adsorption process simulator and, thus, for the development of new pressure and temperature swing adsorption processes using this commercially viable PEI solid amine sorbent for CO2 removal from a variety of gas streams.

Van der Waals corrected DFT simulation of adsorption processes on transition-metal surfaces: Xe and graphene on Ni(111)

The DFT/vdW-WF2s1 method, recently developed to include the van der Waals interactions in the density functional theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe and graphene with a transition-metal surface, namely, Ni(111). In general, the adsorption of rare-gas atoms on metal surfaces is important because it is prototypical for physisorption processes. Moreover, the interaction of graphene with Ni(111) is of great interest for practical applications, for instance concerning the efficient and large-scale production of high-quality graphene; from a theoretical point of view, it is particularly challenging, since it can be described by a delicate interplay between chemisorption and physisorption processes. The first-principles simulation of transition metals requires particular care also because they can be viewed as intermediate systems between simple metals and insulating crystals. Even in these cases the method performs well as demonstrated by comparing our results with available experimental data and other theoretical investigations. We confirm that the rare-gas Xe atom is preferentially adsorbed on the top-site configuration on the Ni(111) surface too. Our approach, based on the use of the maximally localized Wannier functions, also allow us to well characterize the bonds between graphene and Ni(111).